Furnacing process



FURNACING PROCESS Filed Feb, 8, 1919 wvewtoz itatent New. 13, @230 PATENT EARL S. IEGGH, Q15 PHEMDELPHIA, TMINSYLVANIA, ASSIGNOE TU GEE DEVELOENT COMPANY, F PHILADELPHIA, PENNSYLVANIA, A. Gfi llhKDE-A'EEQJH as human.

FUENACING PRDCESS.

Application filed Fe ruary t, 1919. Serial lilo. 275,??7.

To all wlwm z'fimag/ concern:

Be it known that l, CARL S. Focn, a subject of the King of Denmark, residing at Philadelphia, in the county of Philadelphia and State of Pennsylvania, have invented certain new and useful Improvements in Furnacing' Processes, of which't'he following is a specification.

his invention relates broadly to proc- '10 esses for efiecting a conservation of heat in such furnacing operations as are or may-advantageously be carried out in a current of neutral or reactive gas or vapor. A primary object of the invention is to provide processes by means of which a material conservation of heat may be "effected in operations of the above type, while at the same time adjusting and controlling the temperature conditions within the furnace chamber or reaction zone. The invention is applicable to furnacing operations of the most diverse nature, including such metallurgical operations as the oxidation, reduction or desulfurizing of ores; the volatilization of metal values from ores; a wide variety of exothermic and endothermic chemical reactions occurrin at super-normal temperature; the distillation of hydrocarbons, as in the treatment of oil-shales or other oilbear- 3o ing materials; the coking of coals and other carbonaceous materials, etc. For conven-.

ience all such operations occurring at more or less elevated temperatures are designated collectively herein as turnacing operations.

A further object of my invention is to provide a process for the collection and recovery of such components of the ores or other raw materials treated, or derivatives therefrom, as are volat-ilizable under the operating conditions.

For a fuller understanding of my invention reference is made to the accompanying drawing wherein the figure is a diagrammatic elevation of .one form of apparatus suitable for carrying my process into effect.

The essential elements of the assembly illustrated by way of example in the said drawing are a furnace or reaction chamber A, which may be of any type appropriate for the treatment of the particular material in view; one or more gas-cleaning devices or fume-arresters B (shown as two in number) which are required only in case non gaseous particles are to be separated from the gas stream at this point or in case propriate fiues or conduits as clearly illustrated. The system may operate at substantially atmospheric pressure, or at pressures above orbelow atmospheric as may be desirable in particular cases.

It is of course necessary in a closed circulating system ofthis kind to maintain the total volume of circulating gases substantially constant. Therefore in case there. is an evolution of gas in the furnace A, as for example in the coking of coal or the like,

or an increase in the total gas volume due to any other cause, I provide means, t pified by the fans E for withdrawing from t e system a controlled volume of gas corresponding approximately to that evolved or generated in the furnace or otherwise entering thesystem. I Similarly, in case the reaction is one which is accompanied by an absorption of gas, as for example in the roastin of a sulfid ore such as zinc blend to the sul ate, means indicated at G are provided for introducing the required gas in the necessary volume into the system. Such gas may of course be introduced into the system at any desired point -or oints. Obviously this volume-control of t e total gas-content of the system may involve the .introduction of an excess of a reactive gas atone point, and the withdrawal of the excess at another point, as for example when the necessar volume of oxygen for a given reaction is supplied in admixture with nitrogen, as atmospheric air.

As above stated, my invention contemplates 2. conservation of heat, which I bring about by returning to the reaction chamber a part at least of the heat ordinarily lost in the escaping gases. It will be understood that heat may be lost from a system such as has been described in a variety of ways, in-

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eluding radiation and conduction from the exposed walls; in the solid or liquid product discharged from the furnace; and in the escaping gas. Losses by radiation and conduction may of course be minimized by a proper design of the apparatus and by ap propriate heat insulation. Losses in the product discharged from the furnace are readily computed, as a rule are not excessive, and are partly recoverable by various known expedients osses in the escaping gas are as a rule high and it. is one of the ob'ects of my invention to recover a portion at least ofthese last-mentioned losses by returning to the furnace or reaction chamber a sufiicient proportion of the highly-heated exit gases (after separating therefrom any recoverable values) to maintain at a substantially constant quantity the total gas-volume in the system. At the same time I supply 1 heat to or withdraw it from these returned gases in the precise amount necessary to maintain the proper temperaturelimits within'the furnace. lso, I modify the composition of the gases entering the urnace as may be required, as for instance by the introduction, of oxygen (as such or in atmospheric air) in those cases where oxygen is consumed, as in the roasting of sulfid ores, etc.

It will be understood by those skilled in this art that the possibility in a' system of this kind of controlling, quite independently of each other, the temperature and the composition of the clrculating gases, afi'ords the widest latitude in the treatment of ores and other materials. For example oxidizing, neutral or reducin conditions may be main tained at will, w ile at the same time the temperature may be accurately adjusted and controlled. It will of course be understood that the heatbalance of the system will take into account all pertinent factors, including not merely the direct losses mentioned above, but also the heat required for raising all inflowing materials to the operating temperature, the heat requisite for vaporization and not restored to the system by condensation, the heat absorbed by endothermic reactions, and the like. In like manner the heat evolved by exothermic reactions will be considered, and may in certain cases be such as to require positive cooling in the temperature regulator C. On the basis of these principal factors affecting the heat-balance of the system as a whole, it is possible to'determine from available data and with sufiicient exactitude the quantity of heat which must be supplied to or abstracted from the gas stream in the heat-regulator C, in order uniformly to maintain the de' sired temperature in the furnace A.

It will be understood from the foregoing that the invention is not l mited to the use of any specific types of apparatus indicated diagrammatically by the elements A, B, C

and D of the drawing, as the type chosen must of necessity depend on the particular material treated and the treating conditions. For example the fume-arresters B may be merely settling chambers having for their primary purpose the separation of a portion of the dust from the gas-stream before its delivery to the temperature-regulating device C; or they may consist of electrostatic precipitators or other special recovery devices where values are to be recovered at this point.

As one example of the application of my invention to the art of'metallurgy, I will describe the treatment of a com lex ore containing lead, copper, gold and si ver. for recovery of these values. The oxidized ore is mixed with chlorid of sodium or'calcium in proportion sutficient to convert the metal valuesinto chlorids, and fed continuously to the furnace, which may be a rotary kiln, or a mechanical furnace of'the \Vedge type as illustrated in the drawing. An operating temperature in the neighborhood of 900 C. is to be maintained in the furnace. The metals mentioned above are volatilized as chlorids, which pass to the fume-arresters B and are there recovered from the highly heated gases For this purpose the fume-arrester will preferably be an electric precipitator of the well known Cottrell type, suitably heat insulated. Oxygen or air to afford the necessary oxidizing conditions is supplied at The exit gases are returned by the impeller D to the heat regulator C, by which the lost heat is restored (for example by means of oil burners H) the ire-heated gases flowing thence directly to the volatilizing chamber A and so on in continuouscycle. Suiiicient gas is withdrawn at E to maintain constant the circulating volume and will of course be subjected to any appropriate treatment for the recovery of the desired product or products, passing for this purpose to any suitable condensing or recovery system.

In the drawing I have illustrated two symmetrically disposed gas-circuits, and I prefer to use a multiplicity of such circuits in order to secure the best distribution in the furnace. It will be understood, however, that one or several of such circuits may be used.

While the operation of volatilizing metal values, as described above, is one which requires an operating temperature which, as compared with ordinary roasting operations, is relatively high, it may nevertheless be economically practiced in a system of this kind, for the reason that the heat-recovery in tllllfi returned hot gases is correspondingly hig It is impracticable to specify all or even any considerable proportion of the operations to which the invention' may be applied,

but the following will serve as typical examples to which others will be readily added by those skilled in the art:

The distillation of oil-shales or other oilbearing materials in a non-reactive circulating atmosphere comprising the hydrocarbon vapors, the excess volume of vapor bein continuously withdrawn, and a portion 0' the same (or its equivalent in other fuel) burned to supply the required heat increment. Y

The coking of bituminous coal in a nonreactive circulating atmosphere of the coking gases, with similar disposal of the excess The desulfurizing of zinc blend in a circulating atmosphere containing any desired constantly maintained percentage of sulfur dioxid; for instance a concentration of about 8% may be maintained, the excess gas being constantly withdrawn and applied to the production of sulfuric acid.

The decomposition of sulphur hearing materials, as iron pyrites, in a non-reactive circulating atmosphere of sulfur vapor, the excess vapor being condensed at the point B and recovered as molten. sulfur, the pyrites being converted into magnetic sulfid of iron.

The roastin of zinc sulfid to zinc sulfate under control ed temperature conditions of about 300600 (3., in a circulating atmosphere of air, oxygen being supplied to the furnace as required. This is typical of a class of operations, which under proper conditions and with proper furnace design, afford an excess of available heat. and may therefore be carried out in a continuing operation without expenditure of fuel.

My invention is applicable with particular advantage to the treatment of ores and other materials in hearth furnaces, especially continuous-feed single or multiple hearth furnaces, mechanically rabbled. By the application of this invention to such furnaces results may be attained which have practically been attainable heretofore only in furnaces of the mufiie type, to wit:--the heating of materials to a high temperature while avoid.- ing contact of the charge with gases of com bustion; and the volatilization of values without dilution or contamination by com bustion gases. At the same time the present construction is free from the limitation common to all muffle furnaces that the heat must be supplied to the charge through refractory walls of predetermined area. In my con struction, for example, the heat may be rapidly and efficiently transmitted to the circulating gases through metal or other tubes or conducting surfaces in the heat-controller without dilution of the circulating gases, and delivered thence directly to the furnace charge by physical contact of the heated gases therewith.

I claim:

1. Process of recovering volatilizable values from ores or other materials containing the same, comprising passing a current of gas in contact with the charge at a temperature suiiicient to effect volatilization of values therefrom; separating the condensible values from the heated gas stream at an elevated temperature; and returning a portion at least of the heated gas into contact with the charge, while so adjusting the heat content of the portion of the gas so returned as to maintain the charge at the volatilizing temperature 2. Process according to claim 1 in which the ore is subjected to a chloridizing roast in presence of the gas stream.

3. Process according to claim 1 in which the values are recovered by electrostatic precipitation.

In testimony whereof Iafiix my signature.

CARL S. FOGH. 

